This invention relates to a circuit arrangement for driving a MOSFET coupled to one terminal of a load at its source terminal with the other terminal of the load connected to ground potential.
A conventional circuit arrangement of this type is described, for example, in the journal entitled "Siemens Components" 22 (1984), supplement 4, pp. 169. It utilizes the fact that the source potential of a MOSFET having a source load (source follower configuration) changes when being switched on. If the MOSFET is to remain switched on, then the gate potential must be maintained higher than the source potential by at least the turn on threshold voltage. When the MOSFET is fully conductive, the gate potential therefore has to lie above the drain potential by the turn on threshold voltage. In conventional circuits, it is possible to maintain a source follower in a conducting state even when no higher voltage than the drain source voltage source (operating voltage) is available. These circuits utilize a voltage doubling circuit in which a capacitor is charged to the operating voltage by one of the diodes. Additionally, a clocked d-c voltage is applied to the capacitor which charges the capacitor to a voltage which is higher than the operating voltage. The capacitor discharges through the second diode into the gate-source capacitance of the MOSFET and drives it to become conductive.